Cleric Stance
Doing below level 50 dungeons on WHM and switching between Cleric Stance and cures. It was so much fun until I got heal OGCDs which ruined it for me.
Stance Dancing on tanks
Old content not being nothing due to item level increases so it felt good to do well in it
Old hunts not being nothing due to item level increases so that they left bodies everywhere
Positioning bosses
Using cross-class abilities for fun
PLD's old rotation
5.0 AST or earlier where it felt more fun to juggle cards and handle bad RNG cards
Old MNK because I can't act like I have less positionals
Tank raid-wide mit having less range, because it took me quite some time to not bother running close to the party.
Keeping up Blood of the Dragon even though it was easy
Stuff like both Bard dots buffing the damage of Sidewinder, procs working off crit and buffing players MP, it's a background thing but it just felt better knowing that there was more impact from my decisions

So I just have to endure this nostalgia when I'm going through old dungeons or playing jobs that were around then and try to forget it.